Wednesday Feb 23 , 2011

********Molecules and chemistry **************

Molecules are groups of atoms that are bound together, usually by sharing electrons. Chemical reactions change atoms into molecules or change one type of molecule into another.

Here are representations of a few common molecules.

**First two molecules much beloved by college students:

ethanol molecule

caffeine molecule

**Two molecules most everyone uses but most people cuss at:

Methane molecule

Octane molecule

Methane is natural gas, which is commonly used to heat houses and also generate electricity. Octane is one of the main molecules found in gasoline. Unless you own an oilwell or large quantities of Conoco Phillips stock, you probably cuss at these molecules when you need to aquire them.

Chemical reaction example Here are 2 examples of CHEMICAL REACTIONS. *****In a CHEMICAL REACTION, the NUMBER OF ATOMS OF EACH ELEMENT AFTER THE REACTION MUST BE EQUAL TO THE NUMBER OF ATOMS OF EACH ELEMENT YOU STARTED WITH.*****

The number of atoms "in" and "out" is the same, although the MOLECULES DO CHANGE.

Finding the Earth-Sun distance. The modern way to measure the distance to the Sun is to use radar. Radio waves don't bounce off the Sun (they would just get absorbed), but we can bounce radio waves off of Venus and figure the Earth-Venus distance from the "echo" time and the speed of light. From the Earth-Venus distance, and a little trigonometry, we can find the Earth-Sun distance. The average distance of Earth to Sun is an important "yardstick" for astronomers. We call this distance an astronomical unit, or AU.

Power Output of Sun How the heck can we measure the power output (astronomers call this the "luminosity") of the Sun? In everday words, if the Sun were a lightbulb, what is the Sun's wattage? In principle the measurement is easy: we first measure the amount of power from the Sun that passes through a given area at our distance from the Sun. We can then calculate the total amount of Sun's EMR output (in all directions) knowing the area of a sphere with radius equal to our distance. The answer, shown on the slide, might be described (naturally!) as an astronomically big number!

Large electrical generating station. This is the Palo Verde nuclear power plant west of Phoenix, AZ. Using nuclear fission of uranium, this plant produces about 3 GigaWatts of power and supplies much of the electricity for Arizona. A gigawatt is 1 billion watts, or 1 with 9 zeros. Palo Verde is one of the most powerful sources of electricity in the world.

How many plants like this would be needed to equal the power of the Sun? What if we covered the Earth with nuclear power plants? (That would be about 100 million power plants). Would that many power plants produce more power than the Sun? Not even close! You would need to cover 5 MILLION EARTHS with 100 million power plants each to equal the power of the Sun!!!! YIKES!!

200 Million year old fish fossil We know, from fossil evidence, that the Earth has had liquid water oceans for at least 3 billion years. That means that the Sun has been shining with about its same power for that long. If the Sun had been less powerful, the oceans would have frozen. Now, this means that the Sun has produced an enormous amount of energy over its lifetime. IF the Sun was made of coal or oil or TNT (which liberate energy by CHEMICAL reactions) it would only have enough fuel to power it for a few thousand years. Thus, there must be some source of the Sun's power OTHER THAN CHEMICAL PROCESSES.

Examples of the two types of nuclear reactions NUCLEAR REACTIONS differ from chemical reactions as **A NUCLEAR REACTION DOES CHANGE THE NUMBER AND TYPE OF ATOMS**

In nuclear fission, massive nuclei break apart into less massive nuclei. For some elements (uranium and plutonium for example) this fission liberates a lot of energy.

In nuclear fusion, light element nuclei (such as hydrogen) fuse (are bound together) into heavier nuclei. For certain elements, particularly hydrogen, the fusion process also releases enormous quantities of energy.

For equal masses of starting stuff, nuclear processes can liberate 1 to 10 MILLION times as much energy as normal chemical reactions.

E equals m c squared.

Einstein's Inspiration? (Probably not!)

The equation on the helmet of the football player is probably the most famous equation ever. Einstein derived this equation to show how much energy (E) could be obtained by destroying a quantity of mass (m). c is the speed of light.

In nuclear fusion of Hydrogen into Helium, the mass of Helium that is created is about 1% less than the mass of Hydrogen you start with! Mass appears to have been destroyed. The "lost mass" has been turned into energy! As c is a big number, the amount of energy generated by converting even small amounts of matter into energy is very substantial.

This equation is used in advertisements, on T-shirts, etc. It has become a sort of cultural icon refering to someone or something who is really smart- after all, the equation was derived by Einstein, and everyone knows he was one smart dude. I bet most people who use the equation in this way have no clue as to what it actually means!

I am become Death, the destroyer of worlds.. Nuclear bombs use nuclear processes - fission and fusion - to generate enormous explosions. The first nuclear bombs, commonly called "A-bombs", used fast nuclear fission in a heavy element (uranium or plutonium). Some later nuclear bombs, commonly called "H-bombs" - for hydrogen bomb- get much of their energy from nuclear fusion of a light element into heavier element- the same process that powers the Sun and every other star. In (over)simple terms, an H-bomb uses an A-bomb as a "match" to light the fusion "fire".

The largest H-bomb ever detonated was a Soviet device, dubbed "Tsar Bomba" (Emperor of Bombs), tested in 1961, at the height of the Cold War. This device had the explosive energy of 50 *million tons* of conventional explosives (such as TNT)- or a 50 MT (megaton) yield. This picture shows the characteristic mushroom cloud released by a nuclear explosion- this one is from a US bomb about a third as powerful as Tsar Bomba. The mass of superheated gases generated by the explosion rises far into the upper atmosphere, then starts to cool and "fall over", resulting in the "mushroom cloud". This one reached an altitude of 20 or 30 miles - several times as high as Mt Everest or the altitude of a jet.

Of course, the mushroom cloud represents only a tiny portion of the energy released in the explosion- most of the destructive power comes from a blast wave and fireball. Tsar Bomba broke windows 500 miles from the explosion site. Nuclear bombs also scatter deadly radioactive debris far and wide. Exploded in a populated area, such as New York, Tsar Bomba would have killed millions of people in the blink of an eye, and more millions slowly from radiation poisoning.

The first nuclear bomb was exploded on 16 July 1945 in the White Sands area in central New Mexico. Since then, several tens of thousands of nuclear bombs have been made, mostly by the US and Russia. Over 2000 have been exploded in "tests"- mostly to see if the things worked, but also some "tests" were more political in nature. The only nuclear weapons used in war were the two bombs used by the US against the Japanese cities of Hiroshima and Nagasaki in 1945 in WWII. These bombs were not very powerful compared to present day devices, but managed to kill about 100,000 people instantly and a similar number more slowly from radiation.

At the 1945 New Mexico test project director J. Robert Oppenheimer watched the worlds first nuclear mushroom cloud rise. He later said that a line from the Hindu scripture the Bhagavad Gita came to mind as he watched:


I am become Death, the destroyer of worlds.

Test director Kenneth Bainbridge said to Oppenheimer, "Now we are all sons of bitches."

It is estimated that the US has spent $5,000,000,000,000 (5 *Trillion* dollars) on all aspects of its nuclear weapons program since it started during WWII.

Nuclear weapons - may they Rust in Peace!

Hiroshima 1945 The after effects of a nuclear fission chain reaction in a chunk of uranium and plutonium not much bigger than a softball. Of course, there were also German cities that looked like this after Allied bombing. BUT the German cities were destroyed by conventional (CHEMICAL REACTION) explosives, so it took thousands of large (several tons each) bombs, dropped from hundreds of airplanes, to equal the destructive power of a single A-bomb.